Athletic shoes for use in various athletic activities are made up of various shoe sole components such as an outersole, a midsole and an innersole. A material for these shoe sole components is required to be of a light weight, and have a mechanical strength, a rebound resilience and other properties that can suppress deformation due to the long term use, and are durable against severe use conditions. For this, a cross-linked foam of a resin is mainly used for the shoe sole components.
Hitherto, as a material for a shoe sole component, polyurethane, natural rubber or ethylene-vinyl acetate copolymer is used from the point of view of durability, cost and manufacturing restrictions, and they are cross-link foamed when used as a material for a shoe sole component. Of them, a cross-linked foam of ethylene-vinyl acetate copolymer is frequently used.
Although the cross-linked foam of ethylene-vinyl acetate copolymer has excellent characteristics such as strength and cushioning property under a temperature of 20 to 30° C., it poses a problem in that it is hardened and hence has a deteriorated cushioning property under a severe cold for example at −10° C. or lower. In addition, under high temperature environment of 30° C. or higher, the ground is heated to a temperature above the environment and hence the cross-lined foam is excessively softened and has a deteriorated cushioning property. Furthermore, the cross-linked foam has a deteriorated mechanical strength such as tearing strength when it is highly foamed aiming at weight reduction, which may pose a problem in that it cannot be used as a shoe sole.
In order to solve the above problem, Patent Document 1 discloses a cross-linked foam that uses a mixture of ethylene-vinyl acetate copolymer and ethylene-butene copolymer. However, in the existing circumstances, the cross-linked foam of Patent Document 1 has deteriorated strength, cushioning property or other properties under severe cold at a temperature of −10° C. or lower or under high temperature conditions exceeding 30° C., even though it has a lower specific gravity and an improved resilient restoration capability from compression.
Therefore, there is a demand for a shoe sole component that has properties such as strength and cushioning property that are suppressed from being changed even under a wide temperature range from severe cold at −10° C. or lower to high temperature conditions exceeding 30° C.
Patent Document 1: Japanese Patent Application Laid-open No. Hei-11-206406